"Proton Smaller Than Thought—May Rewrite Laws of Physics"

If this holds up, I wonder if physicists will become more humble about their abilities. But I already know the answer:

Proton Smaller Than Thought—May Rewrite Laws of Physics, by Kate Ravilious, National Geographic News: All atoms are made up of nuclei orbited by electrons. The nuclei, in turn, are made of neutrons and protons, which are themselves made of particles called quarks.

For years the accepted value for the radius of a proton has been 0.8768 femtometers, where a femtometer equals one quadrillionth of a meter.

The size of a proton is an essential value in equations that make up the 60-year-old theory of quantum electrodynamics, a cornerstone of the Standard Model of particle physics. The Standard Model describes how all forces, except gravity, affect subatomic particles.

But the proton's current value is accurate only by plus or minus one percent—which isn't accurate enough for quantum electrodynamics, or QED, theory to work perfectly. So physicists have been searching for ways to refine the number.

In a ten-year experiment, a team led by Randolf Pohl of the Max-Planck Institute of Quantum Optics in Garching, Germany, used a specialized particle accelerator... The team knew that firing a laser at the atom before the muon decays should excite the muon, causing it to move to a higher energy level—a higher orbit around the proton. The muon should then release the extra energy as x-rays and move to a lower energy level.

The distance between these energy levels is determined by the size of the proton, which in turn dictates the frequency of the emitted x-rays. But based on the accepted proton radius, the experiment failed to produce x-rays at the anticipated frequency.

In the summer of 2009 the team decided to widen their search to include other possible proton sizes. To their astonishment, the scientists detected x-rays at an assumed proton radius of 0.8418 femtometers—4 percent smaller than expected.

"We were totally surprised and don't have any explanation for it currently," Antognini said. The proton finding won't impact most people's daily lives. But if it proves correct, it means something fundamental is wrong in particle physics. ...

Over the coming weeks physicists all over the world will be scrutinizing the experimental setup and complex calculations, making sure that there are no mistakes. Assuming no errors are found, the scientists may have to get to work rebuilding the Standard Model.